1. Field of the Invention
This invention relates to a liquid friction coupling which comprises a housing that contains a viscous liquid, a shaft coaxially protruding into the housing, two interdigitating sets of inner and outer blades, which are axially slidably mounted on the shaft and in the housing, respectively, and are non-rotatably connected thereto, annular spreading springs, which are disposed between adjacent blades of one of said sets, and an annular piston, which is displaceable and sealed in said hosuing and is operable from the outside of the housing to change the distance between adjacent ones of said blades.
This invention relates also to a motor vehicle which comprises a motor, two driven axles and a planetary gear train, which serves to drive one of said two driven axles and comprises first, second and third torque-transmitting members, wherein said first torque-transmitting member is operatively connected to the motor and the second torque-transmitting member constitutes an output member for driving said one driven axle.
2. Description of the Prior Art
Such a liquid friction coupling is known from AT-A-384,086. The annular piston is adapted to be forced inwardly in the housing from the outside only against the force of the spreading springs by mechanical or hydraulic force and in its axially inner end face is formed with a recess so that a relatively large clearance space is left between that blade which is nearest to the piston and the effective surface of the piston. In that clearance space in the coupling housing, a separation of liquid and air may occur so that the ability to control the coupling by means of the annular piston may be adversely affected. It must be borne in mind that the air tends preferentially to accumulate in said clearance space so that hardly any air will be left between the blades and the inward movement of the piston can control the clutch only by a change of the width of the gap between adjacent blades rather than also by a change of the pressure of the air-liquid mixture in the gaps between adjacent blades. But the change of the width of the gaps is not sufficient in itself so that the known liquid friction coupling can be controlled only within relatively narrow limits.